Sealing glass for magnetic head, magnetic head, and magnetic recording/reproducing device

ABSTRACT

A magnetic head for a magnetic recording/reproducing device to conform to high-density recording, wherein a metal magnetic film with a high saturation flux density is employed and the mechanical strength of the sealing glass for magnetic heads, is improved thereby achieving a high reliability, high performance magnetic head. Also, this is provided a magnetic recording/reproducing device utilizing the magnetic head. 
     Sealing glass for magnetic heads comprising, by oxide conversion, 17.2 to 25 wt % of SiO 2 , 1 to 10 wt % of B 2 O 3 , 58 to 75 wt % of PbO, 0.2 to 7 wt % of at least one of Al 2 O 3  and ZnO, and 0.2 to 5 wt % of at least one of Na 2 O and K 2 O, and a magnetic head and magnetic recording/reproducing device which utilize the sealing glass.

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCTINTERNATIONAL APPLICATION PCT/JP02/01992.

TECHNICAL FIELD

The present invention relates to a magnetic head suitable forrecording/reproducing a large amount of magnetic information for amagnetic recording medium and a magnetic recording/reproducing deviceusing the magnetic head and, more particularly, to sealing glass forbonding a pair of magnetic core halves constituting the magnetic head.

BACKGROUND ART

Recently, magnetic recording media with higher coercive forces have comeinto use as magnetic recording/reproducing devices become downsized andobtain higher capacities. As a magnetic head for high-density magneticrecording which has a sufficient capability of writing signals on suchmedia, a metal-in-gap (MIG) head has been developed. The MIG head is atype of magnetic head in which gap opposing surfaces of a magnetic corehalves are deposited with a metal magnetic film having a high saturationflux density (for example, thin films of magnetic metal materials(hereinafter abbreviated as metal magnetic film) such as Fe—Ta—N,Fe—Ta—Si—N, Fe—Nb—N, Fe—Nb—Si—B—N, Fe—Ta—C, Co—Ta—Zr—Nb, or Co—Nb—Zr—N),and then brought into abutment with each other via a magnetic gapmaterial to be bonded with sealing glass. Conventional magneticsubstances such as permalloy (Fe—Ni alloy) and Sendust (Fe—Al—Si alloy)have a relatively low saturation flux density and therefore cannot beused as the metal magnetic film of a high performance MIG head.

The structure of a MIG head is shown in FIG. 1. Metal magnetic films 3,4 having a high saturation flux density are formed on magnetic gapopposing surfaces of magnetic core halves 1, 2 made of ferrite. Themagnetic gap opposing surfaces are brought into abutment with each othervia a magnetic gap material 5 and then secured with sealing glass 6, 7.

A MIG head is fabricated in a process as outlined in FIG. 2. First, awinding groove 8 and a glass groove 9 are formed on a pair of magneticcore halves 1, 2(a). Then, a truck groove 10 to define the truck widthis formed (b). Further, metal magnetic films 3, 4 (not shown) aredeposited on the ground magnetic gap opposing surfaces, and on top ofwhich a magnetic gap material 5 (not shown) is deposited. Thereafter,magnetic gap opposing surfaces are abutted with each other and sealingglass 6, 7 are disposed in the front gap and the back gap respectively(c), and the pair of the core halves are bonded by heat treatment (d).Thus, a magnetic core block formed by bonding the magnetic core halvesby molding sealing glass is cut to a predetermined size and ground tofabricate a magnetic head chip 11(e). This magnetic chip undergoesprocesses such as base bonding and wire winding to be completed as amagnetic head.

The bonding by means of sealing glass is carried out by softening,cooling, and solidifying the glass by a suitable heat treatment. Duringthis process, to prevent thermal degradation of components such as theabove described metal magnetic film, it is necessary to select sealingglass which can be used at temperatures not exceeding the heat resistanttemperatures of those components. For a MIG head, it is necessary to usesealing glass which can be used in a low-temperature heat treatment nothigher than 600 degrees C.

Generally, when bonding is carried out by softening and fluidizing glassby heating, an actual heat treatment is conducted at a temperaturecalled a working point of the sealing glass to be used. Therefore, forMIG heads, sealing glass of which working point is not higher than 600degrees C. is used. Here, the working point of glass is a characteristictemperature at which the viscosity of the glass reaches 10³ Pa·s thusfluidizing the glass.

However, sealing glass with a working point exceeding the heat resistanttemperatures of the components of the magnetic head can be used as longas the original purpose that is to bond a pair of ferrite cores tofabricate the magnetic head is accomplished. For example, when moldingis conducted by squeezing glass under pressure in a high viscositystate, sealing glass with a high working point may be used.

From the above described reason, sealing glass with an associatedworking point not higher than 650 degrees C. is desired for a MIG head.Sealing glass having such a low working point has been developed, whichincludes SiO₂—B₂O₃—PbO glass systems and B₂0₃—PbO—ZnO glass systems, andlead glass primarily composed of lead oxides (for example, see JapanesePatent Laid-Open No. 7-161011).

As demands for high performance, high reliability magneticrecording/reproducing devices increase recently, further development ofmagnetic heads with a higher record density and higher durability aredesired. To cope with higher record densities, it is necessary torealize a magnetic head having a metal magnetic film having a highsaturation flux density and a structure of a narrower truck width.

As an alloy film of a high saturation flux density suitable forhigh-density recording, an alloy TaMbXcNd is proposed, for example, inJapanese Patent Laid-Open No. 2-208811. In the formula, T is at leastone kind of metal selected from the group consisting of Fe, Co, and Ni;M is at least one kind of metal selected from the group consisting ofNb, Zr, Ti, Ta, Hf, Cr, Mo, W, and Mn; X is at least one kind of halfmetal/semiconductor selected from the group consisting of B, Si, and Ge;N is nitrogen; and a, b, c, and d represent atomic percent where65≦a≦93, 4≦b≦20, 1≦c≦20, 2≦d≦20, and a+b+c+d=100.

Furthermore, a TaMbXcAd alloy film which includes alloys other than theabove described TaMbXcNd alloy has a high saturation flux density and istherefore suitable for high-density recording. In the formula, T is atleast one kind of metal selected from the group consisting of Fe, Co,and Ni; M is at least one kind of metal selected from the groupconsisting of Nb, Zr, Ti, Ta, Hf, Cr, Mo, W, and Mn; X is at least onekind of half metal/semiconductor selected from the group consisting ofB, Si, and Ge; A is N or C; and a, b, c, and d represent atomic percentwhere 65≦a≦93, 4≦b≦20, 0≦c≦20, 2≦d≦20, and a+b+c+d=100.

To accomplish a magnetic head suitable for high-density recording, astructure with a narrower truck width is also needed. To maintain thestrength of such a magnetic head, it is necessary to enhance thestrength of the sealing glass that serves to bond the ferrite cores.Also, since the sealing glass occupies a relatively larger area in thesliding surface of the magnetic head, the sealing glass is prone to wearduring the movement of the magnetic recording medium. Therefore, it isimportant for sealing glass for high performance magnetic heads to havea high strength, and high wear resistance of the sliding surface.

However, there was a problem with conventional sealing glasses in thatthey lack mechanical strength; for example, they are susceptible to wearon the sliding surface, or prone to be fractured or chipped. Forexample, Japanese Patent Laid-Open No. 7-161011 discloses an embodimentof sealing glass composed of 9.9 wt % of SiO₂, 12.2 wt % of B₂O₃, 70.2wt % of PbO, 1.6 wt % of Al₂O₃, 4.5 wt % of ZnO, and 1.3 wt % of Na₂O.However the magnetic head fabricated by using this sealing glass wasfound to have severe wear in the sealing glass or fractures in themagnetic head.

DISCLOSURE OF THE INVENTION

The present invention is directed to solve the above described problem,and its object is to provide a high performance, high durabilitymagnetic head by using an alloy film of a high saturation flux densityas the metal magnetic film and improving a sealing glass, thereby makingits composition mechanically stronger, and a magneticrecording/reproducing device using the magnetic head.

To solve the above problem, the present invention provides a sealingglass for a magnetic head comprising, by oxide conversion, 17.2 to 25 wt% of SiO₂, 1 to 10 wt % of B₂O₃, 58 to 75 wt % of PbO, 0.2 to 7 wt % ofat least one of Al₂O₃ and ZnO, and 0.2 to 5 wt % of at least one of Na₂Oand K₂O.

It is preferable that the sealing glass for a magnetic head mentionedabove, is characterized by comprising not less than 63 wt % of PbO.

Further, it is preferable that the sealing glass for a magnetic headmentioned above is characterized by comprising not less than 0.5 wt % ofAl₂O₃, and not less than 0.5 wt % of ZnO.

Still further, it is preferable that the sealing glass for a magnetichead mentioned above is characterized by comprising not more than 4 wt %of Na₂O and K₂O in total.

Further, the present invention provides a magnetic head which isconfigured such that a pair of magnetic core halves are bonded togetherby use of sealing glass, at least one of the gap opposing surfaces ofsaid magnetic core halves being formed with a metal magnetic film andsaid gap opposing surfaces being abutted with each other via a magneticgap material, wherein said sealing glass is composed of the sealingglass for a magnetic head mentioned above.

Further, said metal magnetic film is composed of a TaMbXcAd alloy film,where T is at least one kind selected from the group consisting of Fe,Co, and Ni; M is at least one kind selected from the group consisting ofNb, Zr, Ti, Ta, Hf, Cr, Mo, W, and Mn; X is at least one kind of halfmetal/semiconductor selected from the group consisting of B, Si, and Ge;A is N or C; and a, b, c, and d represent atomic percent where 65≦a≦93,4≦b≦20, 0≦c≦20, 2≦d≦20, and a+b+c+d=100.

Still further, a magnetic recording/reproducing device of the presentinvention is characterized by comprising the magnetic head mentionedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the magnetic head according to oneembodiment of the present invention.

FIGS. 2( a) to 2(e) are schematic diagrams to illustrate the fabricationprocess of a magnetic head.

FIG. 3 is a perspective view of the rotary drum unit of the magneticrecording/reproducing device according to one embodiment of the presentinvention.

FIG. 4 is a schematic diagram of the driving system of the magneticrecording/reproducing device according to one embodiment of the presentinvention.

DESCRIPTION OF SYMBOLS

-   1, 2 magnetic core half-   3, 4 metal magnetic film-   5 magnetic gap material-   6, 7 sealing glass-   8 winding groove-   9 glass groove-   10 truck groove-   11 magnetic head chip-   12 rotary drum unit-   13 lower drum-   14 upper rotary drum-   15 magnetic head-   16 lead-   17 groove-   18 feed reel-   19 take-up reel-   20, 21, 22, 23, 24, 25 rotary post-   26, 27 slant post-   28 capstan-   29 pinch roller-   30 tension arm-   31 magnetic tape

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of sealing glass for a magnetic head, a magnetic head,and a magnetic recording/reproducing device according to the presentinvention will be described below.

The sealing glass for a magnetic head according to the present inventionis characterized by comprising, by oxide conversion, 17.2 to 25 wt % ofSiO₂, 1 to 10 wt % of B₂O₃, 58 to 75 wt % of PbO, 0.2 to 7 wt % of atleast one of Al₂O₃ and ZnO, and 0.2 to 5 wt % of at least one of Na₂Oand K₂O.

It is more preferable that the above described sealing glass ischaracterized by comprising not less than 63 wt % of PbO.

It is still more preferable that the above described sealing glass ischaracterized by comprising not less than 0.5 wt % of Al₂O₃ and not lessthan 0.5 wt % of ZnO.

It is still more preferable that the above described sealing glass ischaracterized by comprising not more than 4 wt % of Na₂O and K₂O intotal amount.

The reason of limiting each component of the sealing glass will bedescribed in detail referring to embodiments.

The magnetic head according to the present invention is characterized inthat it is configured such that a pair of magnetic core halves arebonded together by use of sealing glass, at least one of the gapopposing surfaces of said magnetic core halves having a metal magneticfilm formed thereon and said gap opposing surfaces being abutted witheach other via a magnetic gap material, and that the sealing glass iscomposed of the above described sealing glass for a magnetic head.

The above described metal magnetic film is composed of a TaMbXcAd alloyfilm, where T is at least one kind of metal selected from the groupconsisting of Fe, Co, and Ni; M is at least one kind of metal selectedfrom the group consisting of Nb, Zr, Ti, Ta, Hf, Cr, Mo, W, and Mn; X isat least one kind of half metal/semiconductor selected from the groupconsisting of B, Si, and Ge; A is N or C; and a, b, c, and d representatomic percent, where 65≦a≦93, 4≦b≦20, 0≦c≦20, 2≦d≦20, and a+b+c+d=100.

Since a high saturation flux density metal magnetic film composed ofTaMbXcAd and sealing glass of a high mechanical strength are utilized,this magnetic head offers high performance required by high-densityrecording with high durability.

The magnetic core, magnetic gap material, etc. of the magnetic head maybe composed of conventional materials that have been used for the samepurpose.

Also, for bonding the back gap side of the magnetic head, which does notslide on the magnetic recording medium, use of the sealing glass of thepresent invention is not a necessity as long as the construction of themagnetic head is possible.

Next, one embodiment of the magnetic recording/reproducing deviceaccording to the present invention will be described.

FIG. 3 is a perspective view of the rotary drum unit of the magneticrecording/reproducing device, and FIG. 4 is a schematic diagram of thedriving system of the magnetic recording/reproducing device. The rotarydrum unit 12 of the magnetic recording/reproducing device shown in FIG.3 has a lower drum 13 and an upper rotary drum 14, and a magnetic head15 is provided on the periphery of the drum unit. The magnetic tapewhich is not shown runs along a lead 16 in a slanted direction withrespect to the rotating axis of the upper rotary drum 14. The magnetichead 15 slides in a slanted direction with respect to the runningdirection of the tape. And a plurality of grooves 17 are provided on theperiphery of the upper rotary drum 14 so that the upper rotary drum 14and the magnetic tape slide with each other stably in a close contactstate. The air sucked into between the magnetic tape and the upperrotary drum is discharged from the groove 17.

The driving system of the magnetic recording/reproducing devicecomprises, as shown in FIG. 4, a rotary drum unit 12, a feed reel 18, atake-up reel 19, rotary posts 20, 21, 22, 23, 24, 25, slanted posts 26,27, a capstan 28, a pinch roller 29, and a tension arm 30. The rotarydrum unit 12 is provided on the periphery with a magnetic head 15 forrecording/reproducing.

The magnetic tape 31 wound on the feed reel 18 is taken up by a take-upreel 19 passing through between the pinch roller 29 and the capstan 28.This rotary drum unit is of an upper rotary drum type and two of themagnetic heads 15 are attached in such a way that they protrude about 20micrometers from the outer periphery of the rotary drum.

Since the magnetic recording/reproducing device of the present inventionis equipped with a high performance, high durability magnetic headaccording to the present invention as the magnetic head 15 forrecording/reproducing, it can reliably perform high-density magneticrecording/reproducing for a digital VTR, for example.

Though, in the above described embodiment, a rotary drum of an upperrotary drum type was taken for an example, it may be of a middle rotarydrum type composed of an upper, middle, and lower drums. Also, though amagnetic tape has been shown as an example, the invention can also beapplicable to disc type media.

Next, the present invention will be described by way of examples.

EXAMPLE 1

As the example and comparative example of the sealing glass for themagnetic head according to the present invention, glasses with variouscompositions shown in Tables 1 to 8 were fabricated to evaluate theworking point of each composition.

The glass was fabricated by preparing and mixing the predetermined rawmaterials, thereafter putting the mixture into a crucible, and meltingit in an electric furnace at 1000 to 1200 degrees C for an hour followedby a rapid cooling.

The viscosity of the molten glass was measured to determine the workingpoint of each composition from the temperature at which the viscosity is10³ Pa*s.

Table 1 shows the glass compositions fabricated to investigate the SiO₂content. Nos. 2 to 4 are examples of the present invention, and Nos. 1and 5 are comparative examples.

Table 2 shows the glass compositions fabricated to investigate thecontent of B₂O₃. Nos. 7 to 9 are examples of the present invention, andNos. 6 and 10 are comparative examples.

Table 3 shows the glass compositions fabricated to investigate thecontent of PbO. Nos. 12 to 14 are examples of the present invention andNos. 11 and 15 are comparative examples.

Table 4 shows the glass compositions fabricated to investigate thecontent of at least one of Al₂O₃ and ZnO. Nos. 19 to 24 are examples ofthe present invention, and Nos. 16 to 18 and Nos. 25 to 27 arecomparative examples.

Table 5 shows the glass compositions fabricated to investigate thecontent of Na₂O and K₂O. Nos. 31 to 36 are examples of the presentinvention, and Nos. 28 to 30 and Nos. 37 to 39 are comparative examples.

TABLE 1 Compara- tive Comparative Example Example Example No. 1 2 3 4 5Glass composition (wt %) SiO₂ 15.1 17.2 22.1 25.0 27.7 B₂O₃ 9.3 6.1 5.02.3 1.0 PbO 68.0 74.3 66.5 65.3 65.1 Al₂O₃ 1.3 1.8 1.7 3.1 5.2 ZnO 4.21.9 1.4 Na₂O 2.1 1.1 2.9 K₂O 0.6 1.7 1.0 Working point (° C.) 560 565605 650 700 Glass wear depth (μm) Metal magnetic film Fe₇₅Ta₁₀N₁₅ 0.590.17 0.15 0.14 — Fe₇₃Ta₈Si₁₃N₆ 0.58 0.15 0.15 0.14 — Fe₇₂Nb₁₂Si₆N₁₀ 0.620.14 0.14 0.14 — Fe₇₆Nb₈Si₂B₁₂N₂ 0.59 0.15 0.15 0.14 —Fe₇₂Ni₁₀W₁Nb₁₀Ge₁N₆ 0.60 0.16 0.16 0.15 — Fe₇₉Ta₉C₁₂ 0.61 0.15 0.15 0.13— Co₉₂Nb₄B₁N₃ 0.58 0.15 0.15 0.15 — Co₇₀Nb₁₀Hf₅B₁N₁₄ 0.60 0.16 0.14 0.15— Co₇₈Nb₆Zr₄B₂N₁₀ 0.60 0.17 0.15 0.14 — Co₆₅Ti₄Ta₄B₂₀N₇ 0.59 0.15 0.160.14 — Co₇₃Mo₇Cr₆Zr₇B₃N₄ 0.62 0.16 0.15 0.15 — Co₇₀Mn₆Nb₇B₁₅N₂ 0.60 0.150.15 0.14 —

TABLE 2 Compara- tive Comparative Example Example Example No. 6 7 8 9 10Glass composition (wt %) SiO₂ 24.7 23.9 18.6 17.3 17.4 B₂O₃ 0.5 1.0 5.810.0 12.0 PbO 65.1 66.3 69.7 67.9 64.0 Al₂O₃ 5.6 3.2 1.8 1.3 0.7 ZnO 1.42.4 1.6 1.4 3.9 Na₂O 1.0 2.9 2.1 1.1 K₂O 1.7 0.3 2.5 0.9 Working point(° C.) 670 650 590 580 575 Glass wear depth (μm) Metal magnetic filmFe₇₅Ta₁₀N₁₅ — 0.14 0.15 0.15 0.47 Fe₇₃Ta₈Si₁₃N₆ — 0.13 0.15 0.16 0.49Fe₇₂Nb₁₂Si₆N₁₀ — 0.14 0.14 0.15 0.50 Fe₇₆Nb₈Si₂B₁₂N₂ — 0.14 0.15 0.150.48 Fe₇₂Ni₁₀W₁Nb₁₀Ge₁N₆ — 0.15 0.15 0.14 0.50 Fe₇₉Ta₉C₁₂ — 0.14 0.140.15 0.48 Co₉₂Nb₄B₁N₃ — 0.14 0.15 0.15 0.49 Co₇₀Nb₁₀Hf₅B₁N₁₄ — 0.15 0.150.16 0.50 Co₇₈Nb₆Zr₄B₂N₁₀ — 0.15 0.14 0.16 0.51 Co₆₅Ti₄Ta₄B₂₀N₇ — 0.150.16 0.15 0.50 Co₇₃Mo₇Cr₆Zr₇B₃N₄ — 0.13 0.14 0.14 0.48 Co₇₀Mn₆Nb₇B₁₅N₂ —0.14 0.14 0.16 0.49

TABLE 3 Compara- tive Comparative Example Example Example No. 11 12 1314 15 Glass composition (wt %) SiO₂ 23.9 23.4 18.6 17.6 17.2 B₂O₃ 8.16.9 5.8 5.5 3.1 PbO 56.1 58.0 69.8 75.0 76.0 Al₂O₃ 5.7 6.0 2.6 0.4 0.7ZnO 1.3 0.9 0.8 Na₂O 2.0 2.8 0.1 1.0 K₂O 2.9 2.0 3.2 0.6 2.0 Workingpoint (° C.) 660 645 590 555 545 Glass wear depth (μm) Metal magneticfilm Fe₇₅Ta₁₀N₁₅ — 0.12 0.15 0.14 0.58 Fe₇₃Ta₈Si₁₃N₆ — 0.13 0.14 0.150.57 Fe₇₂Nb₁₂Si₆N₁₀ — 0.13 0.14 0.15 0.57 Fe₇₆Nb₈Si₂B₁₂N₂ — 0.12 0.140.15 0.59 Fe₇₂Ni₁₀W₁Nb₁₀Ge₁N₆ — 0.13 0.15 0.15 0.58 Fe₇₉Ta₉C₁₂ — 0.130.13 0.16 0.57 Co₉₂Nb₄B₁N₃ — 0.14 0.14 0.15 0.58 Co₇₀Nb₁₀Hf₅B₁N₁₄ — 0.130.14 0.15 0.58 Co₇₈Nb₆Zr₄B₂N₁₀ — 0.13 0.15 0.16 0.58 Co₆₅Ti₄Ta₄B₂₀N₇ —0.13 0.15 0.14 0.59 Co₇₃Mo₇Cr₆Zr₇B₃N₄ — 0.14 0.14 0.15 0.59Co₇₀Mn₆Nb₇B₁₅N₂ — 0.13 0.14 0.15 0.60

TABLE 4 Comparative Comparative Example Example Example No. 16 17 18 1920 21 22 23 24 25 26 27 Glass composition (wt %) SiO₂ 17.5 17.5 17.517.5 17.5 17.5 20.7 20.7 20.7 22.9 22.9 22.9 B₂O₃ 6.1 6.1 6.1 6.1 6.16.1 4.0 4.0 4.0 2.3 2.3 2.3 PbO 74.5 74.4 74.4 74.3 74.3 74.3 66.6 66.666.6 63.5 63.5 63.5 Al₂O₃ 0.1 0.1 0.2 3.3 7.0 4.0 8.5 ZnO 0.1 0.1 0.23.7 7.0 4.5 8.5 Na₂O 0.9 0.9 0.9 0.9 0.9 0.9 1.7 1.7 1.7 K₂O 1.0 1.0 1.01.0 1.0 1.0 1.7 1.7 1.7 1.1 1.1 1.1 Working point (° C.) 560 560 560 560565 565 630 635 630 660 665 655 Glass wear depth (μm) Metal magneticfilm Fe₇₅Ta₁₀N₁₅ 0.53 0.48 0.50 0.18 0.16 0.17 0.14 0.13 0.14 — — —Fe₇₃Ta₈Si₁₃N₆ 0.55 0.47 0.50 0.17 0.17 0.18 0.14 0.13 0.14 — — —Fe₇₂Nb₁₂Si₆N₁₀ 0.54 0.48 0.49 0.17 0.17 0.17 0.15 0.13 0.15 — — —Fe₇₆Nb₈Si₂B₁₂N₂ 0.55 0.50 0.51 0.18 0.17 0.17 0.16 0.14 0.15 — — —Fe₇₂Ni₁₀W₁Nb₁₀Ge₁N₆ 0.56 0.49 0.51 0.17 0.16 0.17 0.15 0.13 0.14 — — —Fe₇₉Ta₉C₁₂ 0.57 0.48 0.50 0.18 0.17 0.18 0.14 0.13 0.15 — — —Co₉₂Nb₄B₁N₃ 0.58 0.49 0.51 0.18 0.16 0.18 0.14 0.13 0.14 — — —Co₇₀Nb₁₀Hf₅B₁N₁₄ 0.55 0.48 0.50 0.18 0.17 0.17 0.15 0.14 0.14 — — —Co₇₈Nb₆Zr₄B₂N₁₀ 0.53 0.50 0.50 0.17 0.17 0.16 0.14 0.13 0.15 — — —Co₆₅Ti₄Ta₄B₂₀N₇ 0.54 0.49 0.50 0.17 0.16 0.17 0.14 0.13 0.15 — — —Co₇₃Mo₇Cr₆Zr₇B₃N₄ 0.55 0.48 0.50 0.18 0.17 0.17 0.15 0.13 0.15 — — —Co₇₀Mn₆Nb₇B₁₅N₂ 0.55 0.50 0.50 0.18 0.16 0.18 0.14 0.13 0.14 — — —

TABLE 5 Comparative Comparative Example Example Example No. 28 29 30 3132 33 34 35 36 37 38 39 Glass composition (wt %) SiO₂ 23.5 23.4 23.423.1 23.1 23.1 18.6 18.6 18.6 17.3 17.3 17.3 B₂O₃ 4.5 4.5 4.5 4.3 4.34.3 5.8 5.8 5.8 6.3 6.3 6.3 PbO 66.8 66.8 66.8 67.6 67.6 67.6 68.8 68.868.8 68.2 68.2 68.2 Al₂O₃ 3.0 3.0 3.0 2.8 2.8 2.8 0.5 0.5 0.5 ZnO 2.22.2 2.2 2.0 2.0 2.0 1.8 1.8 1.8 1.2 1.2 1.2 Na₂O 0.1 0.1 0.2 2.2 5.0 3.06.5 K₂O 0.1 0.1 0.2 2.8 5.0 3.5 6.5 Working point (° C.) 665 660 660 650650 650 575 570 565 550 545 545 Glass wear depth (μm) Metal magneticfilm Fe₇₅Ta₁₀N₁₅ — — — 0.12 0.11 0.13 0.16 0.18 0.18 0.42 0.51 0.55Fe₇₃Ta₈Si₁₃N₆ — — — 0.12 0.12 0.13 0.15 0.17 0.18 0.44 0.50 0.54Fe₇₂Nb₁₂Si₆N₁₀ — — — 0.13 0.13 0.14 0.16 0.18 0.17 0.43 0.50 0.54Fe₇₆Nb₈Si₂B₁₂N₂ — — — 0.12 0.12 0.13 0.16 0.19 0.19 0.44 0.52 0.53Fe₇₂Ni₁₀W₁Nb₁₀Ge₁N₆ — — — 0.13 0.12 0.13 0.16 0.17 0.18 0.42 0.49 0.52Fe₇₉Ta₉C₁₂ — — — 0.12 0.12 0.12 0.15 0.18 0.18 0.43 0.50 0.55Co₉₂Nb₄B₁N₃ — — — 0.12 0.13 0.13 0.17 0.18 0.19 0.44 0.51 0.54Co₇₀Nb₁₀Hf₅B₁N₁₄ — — — 0.13 0.12 0.13 0.16 0.19 0.18 0.42 0.50 0.55Co₇₈Nb₆Zr₄B₂N₁₀ — — — 0.13 0.12 0.13 0.15 0.17 0.17 0.45 0.50 0.54Co₆₅Ti₄Ta₄B₂₀N₇ — — — 0.12 0.12 0.12 0.16 0.18 0.18 0.43 0.51 0.53Co₇₃Mo₇Cr₆Zr₇B₃N₄ — — — 0.13 0.11 0.13 0.17 0.19 0.18 0.44 0.52 0.53Co₇₀Mn₆Nb₇B₁₅N₂ — — — 0.12 0.12 0.13 0.17 0.17 0.18 0.45 0.51 0.55

Moreover, Table 6 shows the glass compositions fabricated to investigatethe content of PbO. Nos. 42 to 44 are examples of the present invention,and Nos. 40 and 41 are comparative examples.

Furthermore, Table 7 shows the glass compositions fabricated toinvestigate the contents of Al₂O₃ and ZnO. Nos. 45 to 50 are examples ofthe present invention, and Nos. 51 to 55 are comparative examples.

Furthermore, Table 8 shows the glass compositions fabricated toinvestigate the contents of Na₂O and K₂O. Nos. 56 to 58 are examples ofthe present invention, and Nos. 59 to 61 are comparative examples.

TABLE 6 Comparat- ive Example Example No. 40 41 42 43 44 Glasscomposition (wt %) SiO₂ 23.4 23.0 20.7 22.1 19.6 B₂O₃ 6.9 5.3 5.0 5.05.8 PbO 58.0 61.3 63.0 66.5 69.7 Al₂O₃ 6.0 2.1 3.1 1.7 2.1 ZnO 0.9 3.53.8 1.9 1.3 Na₂O 2.8 3.2 2.2 1.1 K₂O 2.0 1.6 2.2 1.7 1.5 Working point(° C.) 645 640 635 605 600 Yield (%) Metal magnetic film Fe₇₅Ta₁₀N₁₅ 6371 94 92 97 Fe₇₃Ta₈Si₁₃N₆ 58 65 93 95 96 Fe₇₂Nb₁₂Si₆N₁₀ 60 68 92 92 94Fe₇₆Nb₈Si₂B₁₂N₂ 57 72 93 93 95 Fe₇₂Ni₁₀W₁Nb₁₀Ge₁N₆ 59 66 95 94 96Fe₇₉Ta₉C₁₂ 61 67 92 93 97 Co₉₂Nb₄B₁N₃ 62 69 94 93 96 Co₇₀Nb₁₀Hf₅B₁N₁₄ 6170 94 93 94 Co₇₈Nb₆Zr₄B₂N₁₀ 66 65 93 94 93 Co₆₅Ti₄Ta₄B₂₀N₇ 63 64 92 9595 Co₇₃Mo₇Cr₆Zr₇B₃N₄ 56 62 92 93 95 Co₇₀Mn₆Nb₇B₁₅N₂ 62 68 94 92 94

TABLE 7 Example Comparative Example No. 45 46 47 48 49 50 51 52 53 54 55Glass composition (wt %) SiO₂ 22.1 23.9 18.6 17.3 17.3 18.4 17.7 17.218.7 17.4 17.5 B₂O₃ 5.0 1.0 5.8 6.7 9.5 10.0 5.9 3.1 6.5 6.0 6.1 PbO66.5 66.3 69.7 70.2 68.8 68.1 74.5 75.0 69.9 74.3 73.9 Al₂O₃ 1.7 3.2 1.80.5 2.0 0.5 0.2 1.0 0.7 0.2 ZnO 1.9 2.4 1.6 1.2 0.5 0.5 0.8 0.1 1.0 0.2Na₂O 1.1 2.9 1.0 2.0 0.5 1.0 1.2 0.9 1.1 K₂O 1.7 0.3 2.5 3.1 1.9 0.5 0.42.6 2.7 0.7 1.0 Working point (° C.) 605 650 590 550 580 575 555 550 575570 565 State of glass at sliding surface Metal magnetic filmFe₇₅Ta₁₀N₁₅ ◯ ◯ ◯ ◯ ◯ ◯ X X X X X Fe₇₃Ta₈Si₁₃N₆ ◯ ◯ ◯ ◯ ◯ ◯ X X X X XFe₇₂Nb₁₂Si₆N₁₀ ◯ ◯ ◯ ◯ ◯ ◯ X X X X X Fe₇₆Nb₈Si₂B₁₂N₂ ◯ ◯ ◯ ◯ ◯ ◯ X X X XX Fe₇₂Ni₁₀W₁Nb₁₀Ge₁N₆ ◯ ◯ ◯ ◯ ◯ ◯ X X X X X Fe₇₉Ta₉C₁₂ ◯ ◯ ◯ ◯ ◯ ◯ X X XX X Co₉₂Nb₄B₁N₃ ◯ ◯ ◯ ◯ ◯ ◯ X X X X X Co₇₀Nb₁₀Hf₅B₁N₁₄ ◯ ◯ ◯ ◯ ◯ ◯ X X XX X Co₇₈Nb₆Zr₄B₂N₁₀ ◯ ◯ ◯ ◯ ◯ ◯ X X X X X Co₆₅Ti₄Ta₄B₂₀N₇ ◯ ◯ ◯ ◯ ◯ ◯ XX X X X Co₇₃Mo₇Cr₆Zr₇B₃N₄ ◯ ◯ ◯ ◯ ◯ ◯ X X X X X Co₇₀Mn₆Nb₇B₁₅N₂ ◯ ◯ ◯ ◯◯ ◯ X X X X X

TABLE 8 Comparative Example Example No. 56 57 58 59 60 61 Glasscomposition (wt %) SiO₂ 23.9 18.6 17.3 18.2 18.6 17.3 B₂O₃ 1.0 6.0 6.75.8 6.0 6.7 PbO 66.3 69.6 70.3 68.8 68.6 69.5 Al₂O₃ 3.2 0.5 0.5 0.9 0.50.5 ZnO 2.4 1.3 1.2 1.3 1.3 1.2 Na₂O 2.9 4.0 2.2 4.0 0.8 K₂O 0.3 4.0 2.81.0 4.0 Working point (° C.) 650 570 545 580 570 545 State of glass atsliding surface Metal magnetic film Fe₇₅Ta₁₀N₁₅ ◯ ◯ ◯ X X XFe₇₃Ta₈Si₁₃N₆ ◯ ◯ ◯ X X X Fe₇₂Nb₁₂Si₆N₁₀ ◯ ◯ ◯ X X X Fe₇₆Nb₈Si₂B₁₂N₂ ◯ ◯◯ X X X Fe₇₂Ni₁₀W₁Nb₁₀Ge₁N₆ ◯ ◯ ◯ X X X Fe₇₉Ta₉C₁₂ ◯ ◯ ◯ X X XCo₉₂Nb₄B₁N₃ ◯ ◯ ◯ X X X Co₇₀Nb₁₀Hf₅B₁N₁₄ ◯ ◯ ◯ X X X Co₇₈Nb₆Zr₄B₂N₁₀ ◯ ◯◯ X X X Co₆₅Ti₄Ta₄B₂₀N₇ ◯ ◯ ◯ X X X Co₇₃Mo₇Cr₆Zr₇B₃N₄ ◯ ◯ ◯ X X XCo₇₀Mn₆Nb₇B₁₅N₂ ◯ ◯ ◯ X X X

EXAMPLE 2

Out of the glass having various compositions shown in Tables 1 to 8, theglass having a working point not higher than 650 degrees C. were used asthe sealing glass to fabricate the magnetic head of the configurationshown in FIG. 1.

FIG. 1 shows an example of the configuration of the magnetic headaccording to the present invention, in which metal magnetic films 3, 4with a high saturation flux density are formed on the magnetic gapopposing surfaces of the magnetic core halves 1, 2 made of ferrite, andthese magnetic gap opposing surfaces are abutted with each other via amagnetic gap material 5 and secured with sealing glass 6, 7.

The glass was withdrawn from the molten glass into fibers of a diameterof 0.5 mm and a length of 30 mm to be used as a sealing glass. Mn—Znsingle crystal ferrite was used as the ferrite to form the core halvesof the magnetic head, a TaMbXcAd alloy film of a saturation magneticflux density (Bs) not lower than 1 T as the metal magnetic film, andsilica glass as the magnetic gap material.

In the formula TaMbXcAd, T is at least one kind of metal selected fromthe group consisting of Fe, Co, and Ni; M is at least one kind of metalselected from the group consisting of Nb, Zr, Ti, Ta, Hf, Cr, Mo, W, andMn; X is-at least one kind of half metal/semiconductor selected from thegroup consisting of B, Si, and Ge; A is N or C; and a, b, c, and drepresent atomic percent where 65≦a≦93, 4≦b≦20, 0≦c≦20, 2≦d≦20, anda+b+c+d=100. The composition of the alloy films used in the presentexample is shown in Tables 1 to 8.

Each of the fabricated magnetic heads was subjected to a magnetic taperunning test under conditions of an ambient temperature of 23 degrees C.and a relative humidity of 70%, for 1000 hr to measure a wear depth ofthe sealing glass at the sliding surface from the original state. Thewear depth is preferably not more than 0.2 micrometer. The measuredresults of the wear depth are shown in Tables 1 to 5.

Table 1 clearly shows that when SiO₂ is less than 17.2 wt %, wearresistance is decreased. Also when it is more than 25 wt %, the workingpoint of glass exceeds 650 degrees C., which is therefore notpreferable.

Table 2 reveals that when B₂O₃ is less than 1 wt %, the working point ofglass exceeds 650 degrees C., and when more than 10 wt %, the wearresistance is degraded, which is therefore not preferable.

Table 3 reveals that when PbO is less than 58 wt %, the working point ofglass exceeds 650 degrees C., and when more than 75 wt %, the wearresistance is degraded, which is therefore not preferable.

In order to improve the wear resistance of glass, it is preferable toimprove water resistance in view of practical use. The glass of thepresent invention contains increased amounts of PbO, Na₂O, or K₂O toachieve a low working point. However, on one hand, since the glass haslow water resistance, Al₂O₃ or ZnO is added to improve the waterresistance.

Table 4 reveals that not less than 0.2 wt % of at least one of Al₂O₃ andZnO is preferably contained. However, when the total amount of Al₂O₃ andZnO exceeds 7 wt %, the glass working point may exceed 650 degrees C. orthe glass may be crystallized, which are not preferable.

Na₂O and K₂O as well as PbO have a tendency to lower the working pointof glass.

Table 5 reveals that it is preferable to contain not less than 0.2 wt %of at least one of Na₂O and K₂O. However, when the total amount of Na₂Oand K₂O exceeds 5 wt %, the wear resistance will be degraded, which istherefore not preferable.

As described so far, the sealing glass which has a working point of nothigher than 650 degrees C. and allows fabrication of a magnetic headwith high wear resistance, preferably comprises 17.2 to 25 wt % of SiO₂,1 to 10 wt % of B₂O₃, 58 to 75 wt % of PbO, 0.2 to 7 wt % of at leastone of Al₂O₃ and ZnO, and 0.2 to 5 wt % of at least one of Na₂O and K₂O.

However, even when the working point of sealing glass is not higher than650 degrees C. as described above, if the viscosity of the glass under aheat treatment condition (not higher than 600 degrees C.) in thefabrication process of the magnetic head is too high, the glass may notsufficiently wet the magnetic core halves even when it is squeezed intounder pressure, and thus may not securely seal them.

Table 6 shows the measured results of the yield of the fabricatedmagnetic heads during the sealing process. The yield indicates theproportion of the completed magnetic heads out of 500 magnetic headsfabricated excluding the ones in which sealing is incomplete due to thelack of fluidity of the glass or cracks are produced due to insufficientwettability. PbO has the effect of reducing the viscosity of the glassthereby increasing its fluidity. Therefore it can improve thewettability of the ferrite core by the glass thus improving the yield.Table 6 reveals that to complete the sealing of magnetic core halves ata high yield not lower than 90%, the content of PbO is preferably notless than 63 wt %.

Moreover, when the magnetic tape is driven under a high temperature,high humidity condition, the materials contained in the magnetic tapemay react with the glass compositions thereby causing discoloring orerosion of the glass at the sliding surface of the magnetic head. Sincethese may cause degradation of the mechanical strength of the glass,discoloring and erosion of the glass are preferably prevented. Tables 7and 8 show the result of the running test of each magnetic tape with themagnetic head being under the condition of an ambient temperature of 40degrees C. and a relative humidity of 80% for 150 hours; in the table,the cases in which no changes are observed are marked by a ‘circle’ andcases with discoloration or erosion of the glass by a ‘cross’.

Since Al₂O₃ and ZnO improve the chemical resistance of glass, they canreduce the reaction between the magnetic tape materials and the glass.To achieve this effect, both Al₂O₃ and ZnO are preferably contained.Table 7 reveals that the sealing glass more preferably contains not lessthan 0.5 wt % of Al₂O₃ and not less than 0.5 wt % of ZnO.

Since the high content of Na₂O or K₂O in glass reduces its chemicalresistance, the glass containing of a high content of such substances isprone to be eroded. To prevent this phenomena, as revealed by Table 8,the total amount of Na₂O and K₂O is more preferably not more than 4 wt%.

Industrial Applicability

As described so far, the sealing glass for magnetic heads according tothe present invention has excellent mechanical properties, and thereforea magnetic head utilizing this sealing glass offers excellent durabilityand high reliability conforming to high-density magnetic recording.

Furthermore, since the magnetic recording/reproducing device accordingto the present invention is provided with the above described magnetichead, it can reliably perform recording and reproducing of a largeamount of magnetic information for a magnetic recording medium.

1. Sealing glass for a magnetic head comprising, by oxide conversion, 17.2 to 25 wt % of SiO₂, 1 to 10 wt % of B₂O₃, 58 to 75 wt % of PbO, 0.2 to 7 wt % of at least one of Al₂O₃ and ZnO, and 0.2 to 5 wt % of at least one of Na₂O and K₂O.
 2. The sealing glass for a magnetic head according to claim 1, comprising not less than 63 wt % by oxide conversion of PbO.
 3. The sealing glass for a magnetic head according to claim 1 or 2, comprising, by oxide conversion, not less than 0.5 wt % of Al₂O₃, not less than 0.5 wt % of ZnO, and not more than 4 wt % of Na₂O and K₂O in total.
 4. A magnetic head which is configured such that a pair of magnetic core halves are bonded together by use of sealing glass, at least one of the gap opposing surfaces of said magnetic core halves being formed with a metal magnetic film and said gap opposing surfaces being abutted with each other via a magnetic gap material, wherein said sealing glass is composed of the sealing glass for a magnetic head according to any of claims 1 to
 2. 5. The magnetic head according to claim 4, wherein said metal magnetic film is composed of a TaMbXcAd alloy film, where T is at least one kind selected from the group consisting of Fe, Co, and Ni; M is at least one kind selected from the group consisting of Nb, Zr, Ti, Ta, Hf, Cr, Mo, W, and Mn; X is at least one kind of half metal/semiconductor selected from the group consisting of B, Si, and Ge; A is N or C; and a, b, c, and d represent atomic percent where 65≦a≦93, 4≦b≦20, 0≦c≦20, 2≦d≦20, and a+b+c+d=100).
 6. A magnetic recording/reproducing device comprising the magnetic head according to claim 4 or 5, and a magnetic recording/reproducing device main unit.
 7. A magnetic recording/reproducing device comprising the magnetic head according to claim 5, and a magnetic recording/reproducing device main unit.
 8. Sealing glass for a magnetic head consisting essentially of, by oxide conversion, 17.2 to 25 wt % of SiO₂, 1 to 10 wt % of B₂O₃, 58 to 75 wt % of PbO, 0.2 to 7 wt % of at least one of Al₂O₃ and ZnO, and 0.2 to 5 wt % of at least one of Na₂O and K₂O. 